In general, a primary circuit operated at a low operating voltage and a secondary circuit operated at a high operating voltage exchange signals via insulating elements for the purpose of ensuring the safety or other purposes.
For example, in a gate driver which drives a power semiconductor element such as an IGBT or a MOSFET used for an inverter which converts direct current to alternating current, a signal to turn on and off the gate of the power semiconductor element is transmitted from the primary circuit to the secondary circuit via a photocoupler.
Meanwhile, the signals related to the operating conditions of the power semiconductor are transmitted from the secondary circuit to the primary circuit via a photocoupler.
However, these photocouplers are externally mounted one on the primary circuit and the other on the secondary circuit, and this makes it difficult to downsize the gate driver.